The primary goal of this proposal is to analyze factors which mediate display of parental behavior of doves, with particular attention paid to sex differences in hormonal and non-hormonal bases. The response which will be analyzed is the timing of incubation, a response with circadian rhythmicity which differs in the sexes. The ways in which this timing behavior is altered by hormones, the cues each partner uses to time his or her response, and the role of social factors (e.g., interactions between mates) will be explored. These studies offer a model system for studying how hormonal factors produce fluctuations in sensory and/or sensory-motor processes. Another goal of the proposal is to complete the series of experiments which specify: (1) the actual hormonal changes of the reproductive cycle, (2) factors involved in the initiation of incubation, especially in the male, (3) functional significance of courtship mediated changes in testosterone secretion in the male. This research offers a naturally occurring model system for clarifying more general aspects of the hormone-behavior relationship.